Produce .weak_def_can_be_hidden for some linkonce_odr values

With this patch llvm produces a weak_def_can_be_hidden for linkonce_odr
if they are also unnamed_addr or don't have their address taken.

There is not a lot of documentation about .weak_def_can_be_hidden, but
from the old discussion about linkonce_odr_auto_hide and the name of
the directive this looks correct: these symbols can be hidden.

Testing this with the ld64 in Xcode 5 linking clang reduces the number of
exported symbols from 21053 to 19049.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193718 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 26 insertions, 0 deletions

diff --git a/test/CodeGen/X86/weak_def_can_be_hidden.ll b/test/CodeGen/X86/weak_def_can_be_hidden.ll
new file mode 100644
index 0000000..f78f357
--- /dev/null
+++ b/test/CodeGen/X86/weak_def_can_be_hidden.ll
@@ -0,0 +1,26 @@
+; RUN: llc -mtriple=x86_64-apple-darwin  -O0 < %s | FileCheck %s
+
+@v1 = linkonce_odr global i32 32
+; CHECK: .globl  _v1
+; CHECK: .weak_def_can_be_hidden _v1
+
+define i32 @f1() {
+  %x = load i32 * @v1
+  ret i32 %x
+}
+
+@v2 = linkonce_odr global i32 32
+; CHECK: .globl  _v2
+; CHECK: .weak_definition _v2
+
+@v3 = linkonce_odr unnamed_addr global i32 32
+; CHECK: .globl  _v3
+; CHECK: .weak_def_can_be_hidden _v3
+
+define i32* @f2() {
+  ret i32* @v2
+}
+
+define i32* @f3() {
+  ret i32* @v3
+}